In the first munera recorded at Rome in 264 BCE, Decimus Junius Brutus had 3 pairs of Thracian style gladiators fighting at munera for his father (Livy, Periochae Book 16). That’s 6 men. In 216 Lucius, Marcus, and Quintus Lepidus had 22 pairs of gladiators fight over 3 days for their father, Marcus Aemilius Lepidus (Livy, From the Founding of the City 23.30.15).
In less than 50 years, gladiatorial shows, although nominally help to honour the dead, became a way for elite families to compete with each other for political gain. In 206 BCE the games moved overseas: even before the end of the Second Punic War (in 202BCE) Scipio Africanus the Elder gave a gladiatorial type show for his father and uncle in New Carthage, Spain. (The participants were his soldiers, rather than gladiators, and they were volunteers; Livy, Periochae 28.) The numbers kept increasing: 60 pairs in 183 in the munera for Publius Licinius; 74 pairs in 174 in games given by Titus Flamininus for his father (Livy, From the Founding of the City 41.28).
In the Late Republic (133-31 BCE) spectacles became an increasingly important way for members of the Roman elite to compete for electoral success. As there were only two consuls each year and far more people who wanted and were eligible for taking that office, the competition was fierce. Seats at a gladiatorial show were one nice way to encourage Roman citizens to vote for you. The Greek historian Polybius tells us that even before then, in 160 BCE, that putting on a decent spectacle cost 750,000 sesterces – an immense sum (Histories 31.28.6). Various attempts were made to pass laws to clamp down on the use of munera for such purposes, including barring people from throwing them the year before an election campaign (with some leeway). Nobody paid much attention and being sued for electoral bribery became a common event in many candidates lives. Cicero, the leading lawyer and orator of the Late Republic, had to defend a friend on one such charge. Even though he had passed a law against using spectacles in this way, he still put up a vigourous and successful defence based on tradition:
“But spectacles were exhibited to the people who sat in their tribes, and crowds of the common people were invited to dinner.” Although this, members of the jury, was not done by Murena at all, but done in accordance with all usage and precedent by his friends, still, being reminded of the fact, I recollect how many votes these investigations held in the Senate have lost us, Servius. For what time was there ever, either within our own recollection or that of our fathers, in which this, whether you call it ambition or generosity, did not exist to the extent of giving a place in the circus and in the Forum to one’s friends, and to the men of one’s own tribe?
Cicero, In Defence of Murena 72
Even though towns around them started building permanent, stone amphitheatres, the Romans held off from building one in Rome because they argued it would lead to moral decay. It’s not a very convincing argument, but the fact is that until 29 BCE did the Romans build a (apparently very unsatisfactory) one in the Campus Martius. This was built by Statilius Taurus as the urging of the Emperor Augustus. Caligula started one, but it was never finished. It wasn’t until the Flavian dynasty took the imperial throne and built the Colosseum that Rome had an amphitheatre which reflected her power.
It was opened by Titus with spectacular games:
At the dedication of his amphitheatre and of the baths which were hastily built near it he gave a most magnificent and costly gladiatorial show. He presented a fake sea-fight too in the old naumachia, and in the same place a combat of gladiators, exhibiting five thousand wild beasts of every kind in a single day.
Suetonius, Titus 7.3